I have a function, which receives 2 params: a variable, and a string representation of a data type ('String', 'Object' etc):
function typeChecker(variable, dataType) {
// checks type, returns true or false
}
I want to convert the second parameter to a constructor, so that this expression does not throw an error:
variable instanceof 'Date'
Question: Is it possible to convert any of these:
'String'
'Date'
'Object'
To these:
String
Date
Object
Those constructors all happen to be members of the global object (either window in the browser or global in Node.js), so you could do one of
variable instanceof window['Date']
variable instanceof global['Date']
If your constructor does not exist as a member o the global object, you can check if any prototype in the value's prototype chain is associated with a constructor whose name matches the desired string:
function checkIfValueIsOfTypeName(value, typeName) {
while(value = Object.getPrototypeOf(value)) {
if(value.constructor && value.constructor.name === typeName) {
return true;
}
}
return false;
}
This is more or less how instanceOf operates internally, except instanceOf directly compares constructor to the right-hand value, instead of comparing its name to a string, which is what you want to do.
You can use typeof
console.log(typeof 10);
// output: "number"
console.log(typeof 'name');
// output: "string"
console.log(typeof false);
// output: "boolean"
ìnstanceof is used in the question.
typeChecker({}, Object)is possiblewindoworglobalis a better optiontypeofsince was not sure about performance implications of using instanceof when not necessary.